This disclosure relates to releasable attachment devices of the type used to fasten, retain, or latch together components of an apparatus or a structure that are to be separated or released under controlled conditions.
Hook and loop type separable fasteners are well known and are used to join two members detachably to each other. These types of fasteners generally have two components disposed on opposing member surfaces. One component typically includes a plurality of resilient hooks while the other component typically includes a plurality of loops. When the two components are pressed together they interlock to form a releasable engagement. The resulting joint created by the releasable engagement is relatively resistant to shear and pull forces, and weak in peel strength forces. As such, peeling one component from the other component can be used to separate the components with a minimal applied force. As used herein, the term xe2x80x9cshearxe2x80x9d refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relatively to each other in a direction parallel to their plane of contact. The term xe2x80x98pull forcexe2x80x9d refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to move relative to each other in a direction perpendicular to their plane of contact. Shape memory alloys generally refer to a group of metallic materials that demonstrate the ability to return to some previously defined shape or size when subjected to an appropriate thermal stimulus. Shape memory alloys are capable of undergoing phase transformation in which their modulus, yield strength, and shape orientation is altered as a function of temperature. Generally, in the low temperature, or martensite phase, shape memory alloys can be plastically deformed and upon exposure to some higher temperature will transform to an austenitic phase, or parent phase, returning to their shape prior to the deformation. Materials that exhibit this shape memory effect only upon heating are referred to as having a one-way shape memory alloy. Those materials that also exhibit shape memory upon re-cooling are referred to as two-way shape memory alloys.
Disclosed herein is a releasable fastener system comprising a loop portion comprising a support and a loop material attached to the loop support; a hook portion comprising a support and a plurality of hook elements attached to the hook support, wherein the plurality of hook elements comprises a fiber and a shape memory alloy coating deposited onto a fiber, and wherein shape memory alloy coating deposited onto the fiber comprises a non-axisymmetric coating or deposition of the shape memory alloy about a portion of the fiber surface; and an activation device coupled to the plurality of hook elements, the activation device being operable to selectively provide a thermal activation signal to the shape memory alloy and change the shape orientation, the flexural modulus property, or a combination of the shape orientation and flexural modulus properties of the plurality of hook elements to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.
In accordance with another embodiment, a releasable fastener system comprises a loop portion comprising a support and a loop material attached to the support; a hook portion comprising a support and a plurality of hook elements attached to the support, wherein the plurality of hook elements comprises a fiber and a shape memory alloy coating deposited onto the fiber, and wherein the fiber and the shape memory alloy coating or deposition disposed on the surface of the fiber comprises a non-axisymmetric coating or deposition of the shape memory alloy about a portion of the fiber surface; and means for changing the shape orientation, the flexural modulus property, or the combination thereof of the hook elements to reduce a shear force and/or a pull-off force of an engaged hook and loop portion.
A process for operating a releasable fastener system comprises contacting a loop portion with a hook portion to form a releasable engagement, wherein the loop portion comprises a support and a loop material attached to the support, and wherein the hook portion comprises a support and a plurality of hook elements attached to the support, wherein the plurality of hook elements comprises a fiber and a shape memory alloy coating deposited onto the fiber, and wherein the fiber and the shape memory alloy coating comprises a non-axisymmetric coating or deposition of the shape memory alloy about a portion of the fiber surface; maintaining constant shear and pull-off forces in the releasable engagement without introducing an energy signal; selectively introducing a thermal activation signal to the hook elements, wherein the thermal activation signal is effective to change a shape orientation, a flexural modulus property, or a combination thereof to the plurality of hook elements; and reducing the shear and/or pull off forces in the releasable engagement.
A hook portion for a releasable fastener system comprises a support; and comprising a support and a plurality of hook elements attached to the support, wherein the plurality of hook elements comprises a fiber and a shape memory alloy coating deposited onto the fiber, and wherein the fiber and the shape memory alloy coating comprises a non-axisymmetric coating or deposition of the shape memory alloy about a portion of the fiber surface.
The above described and other features are exemplified by the following figures and detailed description.